It wasn't long ago that tennis teenagers were widely considered close to an endangered species.
Once plentiful, there have been in recent years usually just one or two in the top 100 at any given time, such as now 25-year-old Kei Nishikori or now 22-year-old Bernard Tomic, and frequently none at all.
But that seems to be changing.
This year began with just one teenager, Nick Kyrgios, ranked in the top 100, but now there are four, with Borna Coric, Thanasi Kokkinakis, Hyeon Chung and Alexander Zverev joining Australia's Kyrgios, who has since turned 20. That is the most since 2008, when Juan Martin del Potro, Marin Cilic, Ernests Gulbis and Donald Young were all ranked inside the top 100.
Croatia's Coric, 18, had previously broken into the top 100 and returned there during the first week of the season, but Australia's Kokkinakis, 19; Korea's Chung, 19; and Germany's Zverev, 18, began well below that mark and have risen rapidly. Coric is now No. 33 and can claim wins against Rafael Nadal and Andy Murray, while the other three are ranked in the 70s.
And it may not stop there. Another five teenagers are ranked between 100 and 200, bringing the total for the top 200 to nine -- that tops 2007, when there were eight teenagers in the top 200. The other five are Sweden's Elias Ymer, Jared Donaldson of the United States, Japan's Yoshihito Nishioka, and Russian pair Andrey Rublev and Karen Khachanov.
In the men's singles draw at the US Open, there were 10 teenagers competing -- the most since 1990, when a 19-year-old Pete Sampras won the whole thing. And along with several American 17-year-olds like Stefan Kozlov and Francis Tiafoe limbing the ranks, 15-year-old Canadian Felix Auger Aliassime this year became the youngest player to qualify for an ATP challenger event, in the process became the youngest player on the current ATP rankings.
Having remarked repeatedly on how few young players were coming up behind them, the top names now see a proper wave of new talent rising through the ranks. "We didn't see one generation like this in a while," said Rafael Nadal at the US Open, describing some as champions in the making.
But they will likely take a little longer than him. No teenager has won a Grand Slam since the Spaniard did it as a 19-year-old at the French Open in 2005, when there were five teenagers in the top 100.
That is a big change from the 1980s and the beginning of the 1990s, which saw Boris Becker, Mats Wilander, Stefan Edberg, Michael Chang and Sampras win Slams in their teens.
And the lack of teenagers is just a symptom of a general aging of the tour. The average age of the top 100 at the beginning of the 1990s was a little above 23 years old, but has risen to more than 28 years old during the previous year or two.
Getting to the top also seems to require more experience. The average age of the current top 10 is 29 years old compared to 25 for those ranked between 70 and 100, with the relative youthfulness of the lower group again suggesting a new generation is beginning to push its way up, even if it is not there yet.
The shrinking contingent of young players began to capture attention in 2010, when there were no teenagers in the top 100, and even Roger Federer was stumped.
"There's not a whole lot of promising newcomers," he said at the ATP Masters Cup that year. "I'm not sure we even have a lot of players under 21, 22 in the top 100 ... Maybe the game has become more physical and more mental and that's why players today need more time to break through."
By 2013, there were no teenagers even in the top 250. Slower courts, new technology and the increasingly grueling playing styles they enable have all been pointed to as the reasons older players are dominating the game.
But now, a new generation that has grown up and been trained under these conditions seems to be making the leap. And initial breakthroughs by players like Kyrgios, Coric and Kokkinakis could lead to broader change -- if the US Open junior competition is any indication, it seems to be spurring more teenagers to aim higher.
"I see those guys and I want to get to where they are as soon as possible," said 17-year-old Taylor Fritz, who won the US Open boys' singles.
"They're all very confident and they all know they should be there."
"Seeing other people my age playing well in the pros definitely pushes me and shows me I can do it," said Tommy Paul, 18, a finalist in the boys' singles. "So I've just got to keep working hard and do it."
Simply being precocious is not enough to succeed on the tour these days, however, with players having to keep improving as they make their way up.
But while they still have a long road to travel, the teenagers are at least getting off to a good start again.